Recently, there have been several developments in the area of high through-put screening for catalysts and other reactive chemicals. For example, U.S. Pat. No. 6,030,917, inter alia, discloses methods for the preparation and screening of large numbers of organometallic compounds which can be used not only as catalysts, but also as additives and therapeutic agents. Also, U.S. Pat. No. 5,985,356 discloses methods of preparing and screening polymeric materials in array format. In U.S. Pat. No. 6,030,917, for example, libraries of catalysts and organometallic compounds may be synthesized, screened and characterized by synthesizing a spatially segregated array of ligands, combining the ligands with metal precursors, activating the ligand-metal precursor combination, and thereafter combining the activated compound with a third element, such as an olefin for polymerization. Thereafter the product may be rapidly screened using various characterization techniques.
Co-pending commonly assigned U.S. patent application Ser. No. 09/156,827, filed Sep. 18, 1998 (WO 00/17413, published Mar. 30, 2000) discloses forming an array of components at pre-defined locations and that hydrophobic materials can be used to coat the region surrounding the individual reaction regions on a substrate. In part, the application states that “. . . by choosing appropriate material (e.g., substrate material, hydrophobic coatings, reactant solvents, etc.), one can control the contact angle of the droplet with respect to the substrate surface. Large contact angles are desired because the area surrounding the reaction region remains unwetted by the solution within the reaction region.”
In the specific instance where combinatorial methods are used to screen for polymerization catalysts, polymers are typically the desired end product. Generally speaking when olefins, diolefins, acetylenically unsaturated compounds, or other polymerizable monomers, are polymerized (possibly in array format), discrete amounts of polymer are produced. It is then desirable to screen these polymers to determine if they have desired target properties. Most screening or characterization methods however, particularly those codified as ASTM procedures, require large amounts of polymer to perform the tests and require significant time to measure each sample. The polymers produced in the arrays are typically present in both large numbers and small amounts, and thus many ASTM methods are not practical for characterization. It follows then that with new array based rapid screening technologies, new rapid methods to characterize the products, such as polymers, are now also needed.
The high-throughput screening of polymer films using many different analytical methods (such as scanning Fourier Transform infrared spectroscopy (FTIR)) requires control of the arrangement of the polymer samples on a substrate, as well as control of film properties such as the sample size, the sample thickness, and sample uniformity. Polymer films created through evaporative deposition require some method of confinement of the liquid samples to fixed positions on the substrate. Thicker polymer film preparation, which typically employs multiple cycles of evaporative deposition, requires a method of reproducible deposition to the same position on the substrate.
In attempts to address this problem, multiple drops of polymer in solution may be deposited onto a gold coated silicon wafer. The drops typically run or will not remain in one place, particularly when the solvent is flashed off. This is not acceptable for a rapid screening process where the drops have to be in predictable, reproducible spots on the substrate every time. Also, the drops of polymer may not dry evenly, forming a well or doughnut like structure with the bulk of the polymer dried at the rim of the drop. This too is undesirable, although in some embodiments may be acceptable. Certain characterization techniques, such as FTIR, typically require more polymer in the center of the film for measurements. Hence, for some screening techniques, multiple depositions of the polymeric sample to be tested might need to be made. Thus a means to confine the drops to one area reproducibly, such that multiple depositions could be made in the same spot, is needed.